A refrigeration system sometimes needs to use multiple compressors at the same time. For example, the manifolding of compressors is being used in the air conditioning and refrigeration industry more and more frequently. Compressors connected in parallel have advantages such as convenience in energy modulation, convenience in maintenance of a single shutdown compressor, and low cost. Lubrication oil is indispensable during running of the compressors. However, due to different displacements and different piping designs between the compressors, a compressor, especially a scroll compressor with a low-pressure chamber, may be damaged due to the lack of lubrication oil. Therefore, it is necessary to manage oil levels of multiple compressors. In conventional oil level management, active oil return apparatus are used in the freezing industry. These are not as applicable to commercial or light commercial air conditioning due to its high cost and complex system structure. Or, the oil level may also be managed by way of piping design, but this cannot effectively control the oil level of a compressor.
Thus, the conventional oil level management techniques cannot meet requirements of low cost and high reliability.